Fifteen women of four nationalities were arrested for alleged prostitution in Bangkok's Sukhumvit area during a late-night police raid.
Officers launched the crackdown, targeting prostitution and human trafficking activities on Sukhumvit Soi 4, also known as Soi Nana, about 10.30pm on Tuesday.
The operation resulted in the arrest of 15 women - nine Vietnamese, four Tanzanians, one Kenyan and one Thai. They were initially charged with causing a public nuisance.
Soi Nana, with its many bars and restaurants, is a popular centre of nightlife in Bangkok.
Police suspect Thai and foreign women and transgender people are offering sex services in the area.
